I have a brand new Knights Armament Post Ban M4 upper (this is a take off from a new SR-15 that was registered as a SBR). It is a flat top with T numbered markings and has a 16" M4 profile barrel (with feedramp cuts) with the A2 look alike muzzle device. It also includes the new style KAC 300m folding BUIS. The barrel is chrome lined and it has a true NATO 5.56mm chamber.